This patent document relates to magnetic resonance imaging (MRI) technologies.
MRI is a medical imaging technique used for imaging internal biological structures based on the property of nuclear magnetic resonance (NMR). NMR is a physical property in which the nuclei of atoms absorb and re-emit electromagnetic energy at a specific resonance frequency in the presence of a magnetic field. The absorption and reemission of energy can be dependent on the strength of the magnetic field and the magnetic property of the atoms (e.g., atoms whose nuclei possesses magnetic spin). For example, the different nuclei in a molecule absorb the electromagnetic energy by the magnetic field at slightly different frequencies, e.g., a shift from a reference resonance frequency. This shift can be represented as a field-independent dimensionless value known as the chemical shift. The chemical shift can be quite small (e.g., ˜10−6) and can be reported as ratio in parts per million (ppm), e.g., 106·(measured frequency−reference frequency)/reference frequency.
NMR can be used to determine physical and chemical properties of atoms or molecules such as structure, dynamics, reaction state, and chemical environment of molecules. NMR spectroscopy, also referred to as magnetic resonance (MR) spectroscopy, can be used to obtain high spectral resolution data on organic molecules. For example, MR spectroscopy can be used to obtain high spectral resolution data of fat, but with poor spatial resolution. It is also difficult to analyze the data from MR spectroscopy.